Composite quartz body



March 31. 1925. 1,532,002-

E. THOMSON courosn QUARTZ BODY Filqa oqt. so, 1922 mienne/wey i"` E//hu Tho/77600, i

Patented Mar. 31, 1925.-

UNITEp STATES PATENT OFFICE.

ELIH THOMSON," F SWAIIPSCOTT, MASSACHUSETTS, A SSIGNORf ELEC- TRIO COMPANY, A CORPORATION 0F NEWy YORK.

couPosITE-ouamz BODY.

application med october 30,1932. serial No. 597,964.

To all 'whom vit-may concern: .Be it known that I, ELIHU citizen of the United States, residin at Swampscott, in the county of Essex, i tate 0f Massachusetts, have inventedy certain new and useful Improvements in Composite Quartz Bodies, of which the following'is a specification.

The present invention relates to the pro'-4 duction of articles of' quartz which are particularly adapted to the production of reflectors for scientific instruments, as for example, telescopes in which a light-reflecting surface of constant and accurate focus is desired.

A. great `deal of-trouble has been ex? perienoed in accurate scientific work, particularly in astronomical observations-because of fthe expansion and contraction of reflectors due to changes of temperature. It is necessary to keep reflectorsfonlarge tele scopes in storage rooms in which an even temperature vis carefully .maintained and even when the temperature of the reflector has been allowed to become equalized before taking observations, some blurring of the image occurs due to unavoidable thermal changes in the mirror. .The problem of preserving a true reflecting surface becomes especially great when observations of the sunare made due to the heat imparted to the mirror durin the observation. f

The difficulty o working fused quartz has made it impracticable to secure a plate of and thickness `to serve as a reflector for telescopes. -When a quantityo'f .crude quartz, as sand or crystals, is heated in a mold to fusion, the product is an opaque mass which 40 is filled with innumerable minute cavities 'or bubblessomething like snow when converted into solid ice after partial fusion.

Suche mass also is apt to have an irregular surface and may contain large cavities.

This opaque quartz may be rendered clear but the process is expensive and the result ing product is not easily obtained in large masses. c

In accordance' with my invention, I have provided a reflector of amorphous silica or quart-z glass which consists of a plate of high grade, clear quartz backed by a plate of the more easily formed ppaque quartz.

The accompanying drawings illustrate several embodiments of my invention. Figs.

THOMSON, a

clear, homogeneous quartz of sufiicient size 1 to' 3 show successive stages of manufacture of a mirror beginning with-a base of crude opa ue quartz (Fig. 1 faced with high gra eclear quartz (Fig. 2) the finished product being ground, polished and silvered (Fig. 3) Figs. 4 to 6 illustrate the successive steps in the manufacture of a modift cation in which the base plate of crude quartz is provided with facets to facilitate fusion of the heavy base plate to the thinner face plate and Fig. 7 illustrates in seotion a modification in which the junction of back plate 'and face plate is made on. a curved surface. f

Referring tothe drawing, the quartz mirror preferably is made b first preparin a slab 1 of quartz by the sion in a sita le mold of arenaceous quartz, that is, a good grade of quartz sand. For example, coarse quartz sand may be heated `ina carbon mold to the fusing temperature, about 1760 C., in an electrically heated furnace.- At this temperature the quartz is" rendered soft enough to coalesce.

thinnerlayer 2 of high grade transparent quartz bythe fusion of many small pieces of clear quartz arranged together upon the upper face of the thicker quartz plate. Preferably the plate 1 and the facing layer Q of high grade quartz are heated together in a sultable furnace. The fusion of clear The heavy plate of quartz thus prepared is then fused with the pieces of quartz on the backing plate causes i the pieces to spread out and coalesce. The surface of the article thus prepared is ground as indicated in Fig. 3 and then is. silvered orotherwise coated with a reflecting layer.v

In some cases a plate of transparent quartz is prepared by rolling or pressing pure silicain a plastic state into sheet form. This plate then is attached to a backing yplate of ordinaryopaque quartz. As shown in Figs. 4 to 6, a plate 3, of high grade quartz glass which is free from cavities-or bubbles is attached to a thicker backing plate 4`Which has been provided Withprotuberances or facets 5 by grinding or molding. When the plates 3 and 4 are heated to the 'softening point in a suitable furnace, a mold usually being unnccessar the tips of the protuberances which are illustrated as square pyramids, attach themselves to the plate 3 before the plates 3 and 4 have become so plastic as to become deformed apf ing plate of opaque ground. to provide the facets 5 upon. a curved surface, as shown in Fig. `7. The

lplate 3 which may also be ground to roughly lit the facets 5 is then attached by incipient fusionI as already described. The surface of the plate 3 finally is accurately ground, polished and provided with a reflecting sur face layer.

What I claim as new and desire to secure by Letters .Patent of the United States,

1. An article of manufacture comprising a plate of transparent quartz glass having a surface of regular configuration, and a backartz glass.

2. An article of manufacture comprising a plate of homogeneous quartz glass free from cavities, a backing plate therefor of crude `quartz glass, said plates being united by protuberances'on one of saidplates.'

- 3.` The method of .making a plate of quarts which consists in heating aplate of substantially clear homogeneous uartz in contact with a backing plate o opaque quartz until adhesion occurs.

4.A The method of making `a plate of quartz havinga regular, unbroken surface whlch consists 1n heating quartz sand 1ny a mold to cause coalescence of the particles,

thereby forming an opaque mass, andthen tuberances While leavingmsaid main body otherwise intact.

In witness whereof, I have hereunto set my hand this 27th day of October, 1922.

ELIHU THOMSON.

uartz which consists inl 

